Diabetes linked to increased risk of Alzheimer's in long-term study

Diabetes mellitus was linked to a 65 percent increased risk of developing Alzheimer's disease (AD), appearing to affect some aspects of cognitive function differently than others in a new study supported by the National Institute on Aging (NIA) at the National Institutes of Health. The findings, from the Rush Alzheimer's Disease Center's Religious Orders Study, add to a developing body of research examining a possible link between diabetes and cognitive decline. The results reported today are among the first to examine how certain cognitive “systems”—memory for words and events, the speed of processing information, and the ability to recognize spatial patterns—may be affected selectively in people with diabetes.

The research, by Zoe Arvanitakis, M.D., David Bennett, M.D., and colleagues at the Rush University Medical Center in Chicago, IL, appears in the May 2004 issue of the Archives of Neurology . The investigators are part of the institution's Rush Alzheimer's Disease Center, headed by Dr. Bennett. The AD Center is one of 30 across the U.S. supported by the NIA to study and care for Alzheimer's patients.

“The research on a possible link between diabetes and increased risk of AD is intriguing, and this study gives us important additional insights,” says Neil Buckholtz, Ph.D., head of the Dementias of Aging Branch in the NIA's neurosciences program. “Further research, some currently underway, will tell us whether therapies for diabetes may in fact play a role in lowering risk of AD or cognitive decline.”

Some 824 Catholic nuns, priests, and brothers participating in the Religious Orders Study were followed for an average of 5.5 years. They received detailed clinical evaluations annually, including neuropsychological testing of five cognitive “systems” commonly affected by aging, AD, and other dementias—episodic memory (memory of specific life events), semantic memory (general knowledge), working memory (ability to hold and mentally rearrange information), perceptual speed (the speed with which simple perceptual comparisons can be made, such as whether two strings of numbers are the same or different), and visuospatial ability (the ability to recognize spatial patterns).

Over the study period, 151 of the participants had a clinical diagnosis of AD, including 31 who had diabetes. The researchers found a 65 percent increase in the risk of developing AD among those with diabetes compared with people who did not have diabetes.

In measures of cognitive function, only in the area of perceptual speed was there an association with an increased rate of decline over time, by about 44%, when comparing the diabetes and non-diabetes groups. Since stroke-related changes in the brain were found in a previous study to be tied to a decline in perceptual speed, the researchers could not say whether the link between cognitive decline and diabetes appeared because of the changes in the brain associated with Alzheimer's disease or those of some other common age-related condition like stroke or other vascular complications. Studies looking at pathological or brain imaging data would be needed to address these possibilities.

In other areas of cognition, the rate of change over the time period of the study was no different in the two groups. However, at the start of the study, the baseline cognitive function scores of people with diabetes were lower than those of people without diabetes.

“We found that diabetes was related to decline in some cognitive systems but not in others,” says Dr. Arvanitakis of Rush, the lead author of the report. “Since all participants have agreed to brain donation at their deaths, we will have the opportunity to examine the pathologic basis of the association of diabetes to cognitive decline.” The Rush researchers also expressed their indebtedness to the more than 1,000 nuns, priests, and brothers from across the U.S. participating in the Religious Orders Study.

The NIA is the lead Federal agency conducting and supporting research on Alzheimer's disease and age-related cognitive change. For more information, readers and viewers can visit the NIA's Alzheimer's Disease Education and Referral (ADEAR) Center at www.nia.nih.gov/alzheimers or call toll free 1-800-438-4380. Information on aging generally may be viewed at the NIA's general website at www.nia.nih.gov or by calling the NIA Information Center at 1-800-222-2225.

For information on diabetes, see the website of the National Institute on Diabetes, Digestive, and Kidney Diseases (NIDDK), at www.niddk.nih.gov, or call the National Diabetes Information Clearinghouse, a service of the NIDDK, at 1-800-860-8747.